Method and device for operating a hybrid vehicle

ABSTRACT

A device for the operation of a hybrid vehicle. The hybrid vehicle has a first and a second drive assembly. The drive assemblies in each case drive the hybrid vehicle, alone or jointly in a hybrid type of operation. The first drive assembly is operated with fuel from a fuel tank and a sensor device monitors an amount of fuel in the fuel tank. The device activates a safety operation of the hybrid vehicle if the amount of fuel is smaller than a specifiable value. The device reduces the output of the second drive assembly during the safety operation when a type of operation is being used in which the torque of the second drive assembly is directed oppositely to the torque of the first drive assembly.

RELATED APPLICATION

This patent application is a divisional application of co-pending U.S.patent application Ser. No. 15/104,593, filed Jun. 15, 2016, which was aU.S. National Phase application of International Patent Application No.PCT/EP2014/074582 filed Nov. 14, 2014 and claims priority to GermanPatent Application No. 10 2013 226 621.9 filed Dec. 19, 2013, the entirecontent of each are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to a method, a device and a powertrain foroperating a hybrid vehicle.

Hybrid vehicles already on the market are characterized in that saidvehicles, on the one hand, have a plurality of drive assemblies and, onthe other hand, comprise a control system for implementing an operatingstrategy, which selects a specific type of operation of the two driveassemblies in dependence on the current ambient conditions. The hybridvehicle can thus be driven alone by one of the drive assemblies orjointly by both of the assemblies. There are also types of operationwhich are selected on the basis of energy-related or dynamic advantages.Energy-related advantages can, for example, be achieved with a type ofoperation in which an internal combustion engine is operated at anoptimal operating point while an electric machine is not being used todrive the vehicle. During this time period, the electric machine isoperated as a generator for generating electrical energy and charging abattery or, respectively, providing electrical loads with electricalenergy. Dynamic advantages are, for example, achieved in a type ofoperation in which the right and left wheel of an axle of a vehicle aredriven with different torques or even with opposite torques in vehicleshaving individually driven wheels on a single axle. Using this type ofoperation, the handling of the vehicle can be significantly improvedwhen traversing curves, i.e. when accelerating about the vertical axis.

As mentioned above, the different types of operation are selected as afunction of different ambient conditions. The German patent applicationDE 10 2008 001 669 A1 thus discloses that, when the fuel tank level islow, a vehicle is switched over into a type of operation which enablesthe hybrid vehicle to have a maximum range at a minimum amount of fuelconsumption. In addition, the German patent application DE 199 02 949discloses how to optimize the operation of an internal combustion enginewhen the tank fill level is low. Methods, which are required to thisend, for determining a tank fill level or for detecting a tank that isalmost empty are sufficiently known from the German patent applicationDE 10 2007 030 992 or from the German patent application DE 196 494 84.

If a vehicle is operated, in the fuel tank of which there is no longermuch fuel, the probability increases that a drive assembly operated withfuel unexpectedly malfunctions due to the fuel tank approaching empty orbeing empty. An unexpected failure of a drive assembly leads to anunexpected drop in the driving power or the driving torque of the driveassembly. This can lead to an unexpected and thus critical positive ornegative acceleration of the drive wheel and consequently of thevehicle; and said failure can thus negatively impact the handling of thevehicle. Depending on the type of operation in which a hybrid vehicle isoperated at the moment of the failure of a drive assembly, the loss ofthe driving power can cause the vehicle to accelerate at unexpectedrates which vary in degree and therefore vary in how critical they areto the safety of the vehicle. The loss of the driving power of a driveassembly of a hybrid vehicle can particularly lead to significantlygreater accelerations that are critical to the safety of the vehiclethan is the case with conventional vehicles which are solely operatedwith an internal combustion engine. Hence, the security risk duringoperation of a hybrid vehicle, in the tank of which no longer much fuelis present, can be increased depending on the type of operation beingused.

A technical solution is therefore sought to further secure a hybridvehicle, i.e. to operate said vehicle without an increased securityrisk, even if no longer much fuel is present in the fuel tank of thehybrid vehicle.

SUMMARY OF THE INVENTION

A method is provided for the safe operation of a hybrid vehicle. Thehybrid vehicle has at least one first and one second drive assembly. Thedrive assemblies in each case drive the hybrid vehicle, alone or jointlyin a hybrid type of operation. The first drive assembly is operatedusing fuel from a fuel tank. An amount of fuel in this fuel tank ismonitored. If the amount of fuel is smaller than a specifiable value,then a safety operation of the hybrid vehicle is activated. According tothe invention, the output of the second drive assembly is reduced duringthe safety operation if the hybrid vehicle is driven using a type ofoperation which negatively influences the driving dynamics of the hybridvehicle in the case of a failure of the first drive assembly.

An operating strategy is thus provided for a hybrid vehicle in which theamount of fuel in the fuel tank is constantly monitored. If it isdetermined that less than a predefined amount of fuel is present, asafety operation is activated. This safety operation means that a checkis made to determine in which type of operation the hybrid vehicle iscurrently being operated. If the current type of operation negativelyinfluences the driving dynamics of the hybrid vehicle in the case of afailure of the first drive assembly, the output of the second driveassembly is then reduced during the safety operation.

In so doing, a check is made during the safety operation whether a typeof operation is currently being used which negatively influences or doesnot negatively influence the driving dynamics of the hybrid vehicle inthe case of a failure of the first drive assembly. The so-called loadpoint shift is an example of a type of operation which negativelyinfluences the driving dynamics in the case of a failure of the firstdrive assembly. This type of operation is characterized in that thefirst drive assembly driven with fuel is operated at an optimaloperating point. At this operating point, the first drive assemblydelivers more power than the vehicle currently requires for the driveand operation thereof. This excess power output is received by thesecond drive assembly, particularly an electrical machine operated as agenerator, and converted into electrical energy. In so doing, the seconddrive assembly generates a high torque, which acts in a deceleratingmanner in the opposite direction of the torque of the first driveassembly. Should the first drive assembly now unexpectedly fail, notonly, in this type of operation, does the loss of the torque of thefirst drive assembly act in a decelerating manner on the vehicle in thedirection opposite to the current driving direction, but also thedecelerating torque of the second drive assembly has the same effect.This would lead to a very strong, unexpected deceleration of the vehicleand thus to a negative influence on the driving dynamics that couldimpair the safety of the vehicle. In order to prevent this negativeinfluence to the greatest possible extent, the power output of thesecond drive assembly is reduced if the safety operation is activatedbecause only an amount of fuel is still available in the fuel tank whichis less than a predefined amount.

An example of a type of operation which does not negatively impact thedriving dynamics in the case of a failure of the first drive assembly isthe joint drive of the hybrid vehicle, wherein the first drive assemblygenerates a small portion and the second drive assembly a predominantportion of the drive output of the hybrid vehicle. A smaller portion canparticularly be in this case 5-45% and a predominant portioncorrespondingly 95-55% of the drive output. If the first drive assemblywere to now unexpectedly fail, only the loss of the torque of the firstdrive assembly has a decelerating effect on the vehicle, and the vehiclewould continue to be moved in the same direction by the second driveassembly. This would lead to a very slight unexpected deceleration ofthe vehicle, which, however, would not cause a negative influence on thedriving dynamics that would be critical to the safety of the vehicle.Even if the safety operation is activated because only an amount of fuelis available in the fuel tank which is less than a predefined amount,the drive output of the second drive assembly is not reduced in thiscase because a type of operation which would negatively impact thedriving dynamics of the hybrid vehicle in the case of a failure of thefirst drive assembly is not being used.

This method advantageously facilitates a safer operation of the hybridvehicle even if the vehicle is operated using a type of operation whichwould negatively influence the driving dynamics of the hybrid vehicle inthe case of a failure of the first drive assembly and if the probabilityof an unexpected failure of the first drive assembly is increasedbecause no longer much fuel is present in the fuel tank of the hybridvehicle.

In one embodiment of the invention, the output of the second driveassembly is reduced during the safety operation if a hybrid type ofoperation is used which negatively influences the driving dynamics ofthe hybrid vehicle in the case of a failure of the first drive assembly.

A safe operation of the hybrid vehicle is advantageously facilitatedusing this embodiment even if the vehicle is operated in a type ofoperation which negatively influences the driving dynamics of the hybridvehicle in the case of a failure of the first drive assembly. Hybridtypes of operation are the types of operation, in which the first andthe second drive assembly are simultaneously operated in the hybridvehicle, independently of the direction of the torque acting on theindividual drive assemblies. In hybrid types of operation, the driveassemblies are particularly mechanically coupled directly to therespectively at least one drive wheel, wherein a closed coupling is alsounderstood as a direct mechanical coupling in this context.

In one embodiment of the invention, the output of the second driveassembly is reduced during the safety operation in a type of operation,in which the output of the second drive assembly negatively influencesthe driving dynamics of the hybrid vehicle in the case of a failure ofthe first drive assembly.

A safe operation of the hybrid vehicle is advantageously facilitatedusing this embodiment even if the vehicle is operated in a type ofoperation which negatively influences, in particular additionallynegatively influences, the driving dynamics of the hybrid vehicle in thecase of a failure of the first drive assembly. A, particularlyadditional, negative influence on the driving dynamics of the hybridvehicle is then present if the direction of the torque of the seconddrive assembly is opposite to the direction of the torque of the activefirst drive assembly.

in another embodiment of the invention, the output of the second driveassembly is reduced during the safety operation when a type of operationis used in which the torque of the second drive assembly is directedoppositely to the torque of the first drive assembly.

A safe operation of the hybrid vehicle is facilitated using thisembodiment even if the vehicle is operated using a type of operationwhich additionally negatively influences the driving dynamics of thehybrid vehicle in the case of a failure of the first drive assembly. Anadditional negative influence on the driving dynamics of the hybridvehicle is then present if the direction of the torque of the seconddrive assembly is opposite to the direction of the torque of the activefirst drive assembly.

In another embodiment of the invention, the output of the second driveassembly is reduced during the safety operation when using a type ofoperation, in which the acceleration about the transverse axis, verticalaxis or longitudinal axis of the hybrid vehicle, which takes effect inthe case of a failure of the first drive assembly, is intensified by theoutput of the second drive assembly.

A safe operation of the hybrid vehicle is facilitated in this embodimenteven if the vehicle is operated using a type of operation in which theacceleration about the transverse axis, vertical axis or longitudinalaxis of the hybrid vehicle, which takes effect in the case of a failureof the first drive assembly, is intensified by the output of the seconddrive assembly. The acceleration about the transverse axis, verticalaxis or longitudinal axis of the hybrid vehicle, which takes effect inthe case of a failure of the first drive assembly, is then intensifiedif the direction of the torque of the second drive assembly is oppositeto the direction of the torque of the active first drive assembly. Forexample, the acceleration about the vertical axis, which takes effect inthe case of a failure of the first drive assembly, is increased by theoutput of the second drive assembly if, in vehicles having individuallydriven wheels on a single axle, the right and left wheel of an axle of avehicle are driven using a type of operation having different torques oreven opposite torques. This type of operation is referred to as torquevectoring and is especially used in vehicles having single wheel drives.

In another embodiment of the invention, the output of the second driveassembly is reduced during the safety operation in the case of thehybrid type of operation known as load point shift or in the case oftorque vectoring.

A safe operation of the hybrid vehicle is facilitated using thisembodiment even if the vehicle is operated in the types of operationknown as load point shift or torque vectoring. The distribution of thedrive output on the two drive assemblies in the case of these types ofoperation can be extracted from the previous embodiments.

In another embodiment of the invention, the second drive assembly isswitched off during the safety operation when using a type of operationwhich negatively influences the driving dynamics of the hybrid vehiclein the case of a failure of the first drive assembly.

A safe operation of the hybrid vehicle is advantageously facilitatedusing this method even if the vehicle is operated in a type of operationwhich would negatively influence the driving dynamics of the hybridvehicle in the case of a failure of the first drive assembly and theprobability of an unexpected failure of the first drive assembly isincreased because no longer much fuel is present in the fuel tank of thehybrid vehicle.

A device for the operation of a hybrid vehicle is furthermore provided.The hybrid vehicle has a first and a second drive assembly. The driveassemblies in each case drive the hybrid vehicle, alone or jointly in ahybrid type of operation. The first drive assembly is operated usingfuel from a fuel tank. Provision is made for a sensor device whichmonitors an amount of fuel in the fuel tank. The device activates asafety operation of the hybrid vehicle if the fuel amount is smallerthan a specifiable value. According to the invention, the device reducesthe output of the second drive assembly during the safety operation if atype of operation is used which negatively influences the drivingdynamics of the hybrid vehicle in the case of a failure of the firstdrive assembly.

A safe operation of the hybrid vehicle is advantageously facilitated bymeans of this device even if the vehicle is operated in a type ofoperation which would negatively influence the driving dynamics of thehybrid vehicle in the case of a failure of the first drive assembly andthe probability of an unexpected failure of the drive assembly isincreased because no longer much fuel is present in the fuel tank.

A powertrain for a hybrid vehicle comprising a first and a second driveassembly is furthermore provided. The drive assemblies in each casedrive the hybrid vehicle, alone or jointly in a hybrid type ofoperation. The first drive assembly is operated using fuel from a fueltank. The powertrain comprises a sensor device which monitors an amountof fuel in the fuel tank and a device which activates a safety operationof the hybrid vehicle if the amount of fuel is smaller than aspecifiable value. According to the invention, the device reduces theoutput of the second drive assembly during the safety operation if atype of operation is used which negatively influences the drivingdynamics of the hybrid vehicle in the case of a failure of the firstdrive assembly.

A safe operation of the hybrid vehicle is advantageously facilitated bymeans of this powertrain even if the vehicle is operated in a type ofoperation which would negatively influence the driving dynamics of thehybrid vehicle in the case of a failure of the first drive assembly andthe probability of an unexpected failure of the drive assembly isincreased because there is no longer much fuel present in the fuel tankof the hybrid vehicle.

In one embodiment of the invention, the first drive assembly is aninternal combustion engine and/or the second drive assembly is anelectrical machine.

The internal combustion engine is advantageously operated with fuel andthe electrical machine is supplied with electrical energy. When theamount of fuel becomes less, the electrical machine can thusindependently drive the vehicle.

It goes without saying that the features, properties and advantages ofthe method according to the invention correspondingly apply to or can beapplied to the device according to the invention or, respectively, tothe powertrain and vice versa.

Further features and advantages of embodiments of the invention ensuefrom the following description with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows schematically a hybrid vehicle comprising a device for theoperation of a hybrid vehicle; and

FIG. 2 shows schematically a method for the operation of a hybridvehicle.

In the figures, identical and functionally identical elements, featuresand components—provided that nothing else is specified—are in each caseprovided with the same reference signs. It goes without saying thatcomponents and elements are not necessarily depicted true to scale inthe drawings for reasons of clarity.

Further possible configurations, modifications and implementations ofthe invention also do not comprise explicitly stated combinations offeatures of the invention which have been previously described or willbe described below.

DETAILED DESCRIPTION

FIG. 1 shows schematically a hybrid vehicle 20 comprising a front axle80 and a driven rear axle 90. The hybrid vehicle includes a powertrain70 comprising a first and a second drive assembly 30, 40, a device 10and a sensor unit 60. A first drive assembly 30 and a second driveassembly 40 can be mechanically coupled and jointly drive the rear axle90 of the hybrid vehicle. The device 10 is designed to actuate the twodrive assemblies 30 and 40. To this end, the device 10 in each caseparticularly specifies a rotational speed (n) and a torque (Nm) or,respectively, an output (W) for the two drive assemblies 30 and 40. Inorder to ensure a safe operation of the hybrid vehicle 20, the amount offuel in a fuel tank 50 is constantly monitored by means of a sensordevice 60. If only a small amount of fuel is still available in the fueltank 50 for the operation of the first drive assembly 30, the device 10then switches on a safety operation. While the safety operation isactivated, the device 10 reduces the output of the second drive assembly40 in a type of operation which negatively influences the drivingdynamics of the hybrid vehicle 20. The hybrid vehicle schematicallydepicted in FIG. 1 comprises, for example, a so-called parallel hybriddrive as a powertrain topology, said parallel hybrid drive comprising aninternal combustion engine as the first drive assembly 30 and anelectrical machine 40 as the second drive assembly. The invention is,however, independent of the powertrain topology used and can therefore,for example, also be implemented in the case of axle-split orpower-split hybrid powertrain topologies or in the case of all otherpowertrain topologies.

FIG. 2 shows a method 110 for the safe operation of a hybrid vehicle 20.After starting the method in step 140, the amount of fuel which issituated in the fuel tank 50 is determined in step 120. In the followingcomparison step 150, the determined amount of fuel is compared to aspecifiable value. If the amount of fuel is greater than the specifiablevalue, the method jumps back to step 120 for the renewed determinationof the amount of fuel. If the amount of fuel is smaller than thespecifiable value, a device 10 activates a safety operation 130. Whilethe safety operation is activated, the device 10 reduces the output ofthe second drive assembly 40 if a type of operation is being used whichnegatively influences the driving dynamics of the hybrid vehicle 20. Inthe following step 160, the amount of fuel is determined analogously tostep 120. In the succeeding comparison step 170, the determined fuelamount is compared to a specifiable value. If the amount of fuel isgreater than the specifiable value, the device 10 deactivates the safetyoperation and the method jumps back to step 120 for the reneweddetermination of the fuel amount. If the fuel amount is smaller than thespecifiable value, the method jumps back to step 130, in which thedevice 10 further maintains the safety operation 130. While the safetyoperation is activated, the device 10 reduces the output of the seconddrive assembly 40 if a type of operation is being used which negativelyinfluences the driving dynamics of the hybrid vehicle.

What is claimed is:
 1. A device (10) for the operation of a hybridvehicle (20), wherein the hybrid vehicle (20) has a first (30) and asecond (40) drive assembly, wherein the drive assemblies (30, 40) ineach case drive the hybrid vehicle (20), alone or jointly in a hybridtype of operation, wherein the first drive assembly (30) is operatedwith fuel from a fuel tank (50) and a sensor device (60) monitors anamount of fuel in the fuel tank (60), wherein the device (10) activatesa safety operation (130) of the hybrid vehicle (20) if the amount offuel is smaller than a specifiable value, characterized in that thedevice (10) reduces the output of the second drive assembly (40) duringthe safety operation (130) when a type of operation is being used inwhich the torque of the second drive assembly (40) is directedoppositely to the torque of the first drive assembly (30).
 2. The deviceaccording to claim 1, characterized in that the first drive assembly(30) is an internal combustion engine and the second drive assembly (40)is an electrical machine.
 3. The device according to claim 1,characterized in that the first drive assembly (30) is an internalcombustion engine.
 4. The device according to claim 1, characterized inthat the second drive assembly (40) is an electrical machine.
 5. Thedevice according to claim 1, characterized in that the second driveassembly (40) is switched off during the safety operation (130).
 6. Apowertrain (70) for a hybrid vehicle (20) comprising a first (30) and asecond (40) drive assembly, wherein the drive assemblies (30, 40) ineach case drive the hybrid vehicle (20), alone or jointly in a hybridtype of operation, wherein the first drive assembly (30) is operatedwith fuel from a fuel tank (50), wherein the powertrain (70) comprises asensor device (60) which monitors an amount of fuel in the fuel tank(50) and a device (10) which activates a safety operation (130) of thehybrid vehicle (20) if the amount of fuel is smaller than a specifiablevalue, characterized in that the device (10) reduces the output of thesecond drive assembly (40) during the safety operation (130) when a typeof operation is being used in which the torque of the second driveassembly (40) is directed oppositely to the torque of the first driveassembly (30).
 7. The powertrain according to claim 6, characterized inthat the first drive assembly (30) is an internal combustion engine andthe second drive assembly (40) is an electrical machine.
 8. Thepowertrain according to claim 6, characterized in that the first driveassembly (30) is an internal combustion engine.
 9. The powertrainaccording to claim 6, characterized in that the second drive assembly(40) is an electrical machine.
 10. The powertrain according to claim 6,characterized in that the second drive assembly (40) is switched offduring the safety operation (130).